data StaV s a = StaF (s -> (s,a))
instance Functor (StaV s) where
  fmap f (StaF g) = StaF (\s ->  let (s2,a) = g s
                               in (s2, f a))
  
instance Applicative (StaV s) where
  pure a = StaF (\s -> (s,a))
  StaF sf1 <*> StaF sf2 = StaF (\s -> let (s2, f) = sf1 s
                                          (s3, a) = sf2 s2
                                      in (s3, f a))

instance Monad (StaV s) where
  (StaF sf1) >>= f = StaF (\s -> let (s2, a) = sf1 s
                                     StaF sf2 = f a
                                     (s3, b) = sf2 s2
                                 in (s3, b))


get = StaF (\s -> (s,s))
set a = StaF (\s -> (a,()))

run (StaF f) s = snd(f s) 

factS n = do set 1
             mapM_ prinasob [1..n]
             res <- get
             return res

prinasob x = do a <- get
                set $ a*x